1. Field of Endeavor
The invention relates to a gas turbine with annular inner and outer shells of an annular combustion chamber, to the closure of the shell segments, and to a method for repairing this closure.
2. Brief Description of the Related Art
There are basically several different approaches for designing gas turbine combustion chambers. One of these is to use annular combustion chambers, and the present invention relates to this. These are annular combustion chambers which are arranged between the compressor and turbine essentially rotationally symmetrically around the rotor of the gas turbine. A combustible gas mixture is introduced via at least one burner into the annular combustion chamber, burns in the latter and flows as an annular stream into the turbine. The essentially annular space is delimited inwardly, that is to say toward the rotor side, by what is known as an inner shell, and is delimited outwardly by what is known as an outer shell. On account of the high temperatures and the generation of heat in the combustion chamber, the shells are exposed to high thermal loads. In order to ensure a sufficient service life in spite of the high heat load, annular combustion chambers having various cooling methods have been developed, which, moreover, are mostly combined with heat protection layers or protective shields.
EP 1312865 proposes an annular combustion chamber which is constructed from shells and the shells of which are connected to one another via flange-like connection regions.
Shells or half shells connected by flanges have the inherent problem that the regions of the parting lines behave differently in thermal terms from the free shell regions without a flange, and therefore the thermal expansions are different from those in the free wall region. This may lead to distortion particularly in the case of thin-walled shells. A distortion of the shells may vary the height of the cooling ducts located on the shell side facing away from the hot gas and consequently may influence the routing of the cooling air and the cooling efficiency. Moreover, the distortion may lead to stresses, crack formation, or mechanical failure of the parts.
In spite of the cooling and of the heat protection layers, the walls of the combustion chamber which face the combustion chamber inside are parts in which the service life is critical. So as not to have to exchange the entire parts if these critical parts are damaged, various repair methods have been developed. EP 1267127 describes repair methods for the exchange of combustion chamber segments, in particular of shells. In this case, the cutting out of portions of the combustion chamber walls and their replacement and also the welding in of replacement pieces are described.
One disadvantage of welding repairs is that the material properties in the region of the weld seam are usually reduced. In addition, there is the problem of applying high-quality heat protection layers to a weld seam. This applies particularly to repairs which are carried out on the spot, that is to say, in the power station, without good access to the components and without optimal boundary conditions for applying the protective layers. The result of this is that, after the repair has taken place, weld seams constitute a weak point in the continual operation of the gas turbine and often no longer achieve the desired service life. Moreover, the application of a high-quality permanent heat protection layer (Thermal Barrier Coating, TBC) leads to high additional costs and time delays in the repair.